Bücker Bü 131 Jungmann CASA 1.131L

The CASA 1.131L is the most elusive subversion of the Spanish Jungmann family. The only definition in the sources consulted comes from the history of Bücker aircraft that Steve Beaver takes from the Air Britain Digest: the first CASA 1.131s, designated E.3B by the Spanish Air Force, appeared in 1938 with the German Hirth HM 504; from the 201st aircraft onwards the 125 hp ENMA Tigre G.IVA was installed and those aircraft were the CASA 1.131Es; production continued until 1960, when some 500 had been built, and "some" of them had 150 hp ENMA Tigre G.IVB engines and were designated CASA 1.131L. No source says how many there were, when they began, or whether they were built that way or re-engined later, and this page does not fill that gap with figures from the 1.131E or from the Hirth-engined CASA 1.131.

The letter should not be confused with Lycoming. Many surviving Jungmann now fly with 150 hp Lycoming O-320 or 180 hp O-360 engines, but those are civil conversions made after retirement; the source that defines the 1.131L ties it to the Tigre G-IVB. The English Wikipedia article on the Elizalde Tigre IV —also known as the ENMA Tigre IV, a four-cylinder inverted air-cooled inline engine that Elizalde designed shortly after the Spanish Civil War— separates the 93 kW (125 hp) IVA from the 110 kW (150 hp) IVB and lists the G-IV A, G-IV A2, G-IV A5, G-IV B and G-IV B5 designations, with the codes G-4 (L)-00-125 and G-4 (L)-00-150. The German Wikipedia confirms that of the more than 550 CASA 1.131s, 200 had the HM 504 and the rest the 125 hp Tigre G-IV A or the 150 hp G-IV B. The CASA Jungmann Research Team adds that the Tigre was built in six versions of 125 and 150 hp, the latest capable of inverted flight and fitted with a starter and generator; it does not say which of them the 1.131L used.

Sources on the last production batches point the same way without naming the subversion. According to the Aviationsmilitaires.net forum, the 100 Tigre-engined aircraft of 1948 to 1951 (c/n 1001 to 1100) were followed by batches of 100 in 1953 (2001 to 2100), 50 in 1957, 50 in 1961 and 30 in 1963 (2201 to 2230), and some re-engined aircraft were given new serials. The Fundación Aérea de la Comunidad Valenciana explains that the aircraft of the so-called 2,000 series originally had the more powerful Tigre G-IV A5 and a structurally reinforced fuselage, with a higher empty weight and wider aerobatic capability; but it calls them C-1131E and gives 125 hp for the G-IV A5. Linking that series to the 1.131L would be an inference that no source makes.

Where the designation does live on is in the survivors. The Real Aero Club de España reported on the work of Paco Rivas, who for almost 15 years tried to identify every CASA 1.131L that survived its retirement from the Spanish Air Force, later joined by researcher Johnny Comstedt and American pilot Brian Karli; the first edition listed more than 90 examples identified by a photo of their manufacturer's plate, the only valid proof. The second edition, of January 2023, is titled "CASA 1.131L Jungmann all over the world" and explains that fuselages were swapped during overhauls, so many aircraft fly under a wrong identity; those converted from Hirth to Tigre carry two plates. The list applies the 1.131L name to the whole surviving population, with build years from 1951 to 1963 and rebuilt airframes such as E.3B-153 (now G-BPTS, 1943/57): among them EC-ERP, operated by the Fundación Infante de Orleans, Karli's own N4261C, G-BHPL in Luftwaffe markings and N91627, built in 1961, at the Early Birds museum of the Dutch Stichting Vroege Vogels foundation.

The engine survives too. In July 2009 about 30 Tigre IV engines were still airworthy in Britain, all powering CASA 1.131s, and another 30 Tigre G-IV B engines were under restoration by the Polish company Air Res Aviation for Jungmann it restores. According to the research team, the Spanish Air Force withdrew its last Bücker in 1988.

Data not found in the sources consulted: number of aircraft designated 1.131L, dates of entry into and withdrawal from service, whether they were new-build or re-engined, and weight and performance figures specific to the subversion.